Does anyone use the "air on demand" compressors with your mill?

[l u k e]

The type you see on construction sites, if so what model do you use? I have a traditional compressor but have been thinking about going to an air on demand system when I get my first Haas.

[Geof]

Aren't all compressors 'air on demand'? They turn off when the upper limit pressure is reached and turn back on when the lower limit pressure is reached.

[Donkey Hotey]

I wouldn't even try. If air is interrupted for a second, the machine will stop the program and throw an alarm. And the spindle uses continuous air (not just during tool changes). So the compressor will be running all the time anyway.

You're thinking in absolutely the wrong direction. You want the biggest honkin' compressor you can get. If I knew five years ago, what I know now, I would have bought a rotary (screw) compressor and a drier. They really aren't that much money in the grand scheme of things and they make your life much easier.

[l u k e]

"On demand" units normally have extremely small tanks. They build high pressure very fast and don't rely on volume to stay ahead of the supply of air that is being used.

[l u k e]

I'm not suggesting that the unit shown is what I want to use, I'm just giving an example. I've been told that the technology in compressors has come a long way for this type of outfit, I’m just checking to see if it's suitable in this regard.

[l u k e]

Originally Posted by Donkey Hotey I would have bought a rotary (screw) compressor and a drier. They really aren't that much money in the grand scheme of things and they make your life much easier.

What are the advantages of the rotary units? I have never heard of one before now. Any recommendations for brand names to look into?

[dertsap]

Originally Posted by l u k e What are the advantages of the rotary units? ?

noise to start with

[Donkey Hotey]

Rotary compressors are quiet. I've been standing next to huge ones at Westec and they made no more noise than a swamp cooler.

I have a Husky 2-stage, V-twin, 80 gallon compressor (15 SCFM @90 PSI) and that stupid thing runs about 30-50% of the time when the spindle is running. And compressed air creates moisture (hence the need for a drier).

Do an eBay search for ROTARY COMPRESSOR and you'll find plenty of brands and examples to get you started. Most of them are huge (and more than you need). I would look for 5-7 hp units.

[fpworks]

Capacity, low maintenance, and long life are the main advantages. Plus they're very quiet. I can easily have a normal conversation standing while leaning against our 5 hp or our 15 hp unit.

FYI, our 5 hp unit can deliver ~17 CFM, and our 15 hp can deliver ~54 CFM all day long, every day, and not limited by a 40-50% duty cycle that is common with reciprocating compressors.

They are pricey, but I think they are worth it. Atlas Copco compressors are available rebadged as Quincy or Chicago Pneumatic for some nice prices.

[l u k e]

Cool! Thanks guys.

[dradef]

Just curious, these at the show, how huge are you talking? Ours seems noisy. It is a fairly new Quincy 75hp screw and matching air dryer. It seems like it shouldn't be as loud as it is with it being in a fully enclosed insulated case.

I bring it up because last week something in the compressor's oil cooling system went down and we had to run on one of our diesel portable units parked outside. Was really strange how much quieter it was in the plant with the normal compressor not running.

Expecting too much from such a large unit?

[pebbert]

Our 20 HP rotary screw while much quieter than the 10HP piston it replaced is not what I would consider "quiet".

I wouldn't want it inside our building unless it was behind a wall. A 75hp unit would be even worse.

One thing that hasn't been mentioned about the rotary screw types is they aren't meant for intermittent service. Most of them run constantly with an internal valve that shuts on and off to compress air or idle.

Our 20hp unit pulls 50A while compressing and 35A at idle. You should only use these types if you have a fairly consistent CFM ( cubic feet per minute) use. Otherwise you are going to pay a lot of money in electricity.

I wouldn't buy one that was more than 2X your CFM use. Example, if your using 30CFM don't buy a rotary compressor that puts out more than 60CFM or your wasting your money. Ideally you would be 80%+ utilization.

Piston compressors turn off when they reach pressure, zero electrical use.

Rotary compressors idle. Our 20HP draws 14500W at idle, at $0.10/hr for electricity, that's $1.45/hr to do nothing. If it's at 50% duty cycle, it cost's
1.45*4hrs/day*260days= $1500/yr idling.